/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.state;



import com.bff.gaia.unified.sdk.annotations.Experimental;

import com.bff.gaia.unified.sdk.annotations.Experimental.Kind;

import com.bff.gaia.unified.sdk.annotations.Internal;

import com.bff.gaia.unified.sdk.coders.Coder;

import com.bff.gaia.unified.sdk.transforms.Combine;



import java.io.Serializable;



/**

 * A specification of a persistent state cell. This includes information necessary to encode the

 * value and details about the intended access pattern.

 *

 * @param <StateT> The type of state being described.

 */

@Experimental(Kind.STATE)

public interface StateSpec<StateT extends State> extends Serializable {



  /**

   * <b><i>For internal use only; no backwards-compatibility guarantees.</i></b>

   *

   * <p>Use the {@code binder} to create an instance of {@code StateT} appropriate for this address.

   */

  @Internal

  StateT bind(String id, StateBinder binder);



  /**

   * <b><i>For internal use only; no backwards-compatibility guarantees.</i></b>

   *

   * <p>Perform case analysis on this {@link StateSpec} using the provided {@link Cases}.

   */

  @Internal

  <ResultT> ResultT match(Cases<ResultT> cases);



  /**

   * <b><i>For internal use only; no backwards-compatibility guarantees.</i></b>

   *

   * <p>Given {code coders} are inferred from type arguments defined for this class. Coders which

   * are already set should take precedence over offered coders.

   *

   * @param coders Array of coders indexed by the type arguments order. Entries might be null if the

   *     coder could not be inferred.

   */

  @Internal

  void offerCoders(Coder[] coders);



  /**

   * <b><i>For internal use only; no backwards-compatibility guarantees.</i></b>

   *

   * <p>Validates that this {@link StateSpec} has been specified correctly and finalizes it.

   * Automatically invoked when the pipeline is built.

   */

  @Internal

  void finishSpecifying();



  /** Cases for doing a "switch" on the type of {@link StateSpec}. */

  interface Cases<ResultT> {

    ResultT dispatchValue(Coder<?> valueCoder);



    ResultT dispatchBag(Coder<?> elementCoder);



    ResultT dispatchCombining(Combine.CombineFn<?, ?, ?> combineFn, Coder<?> accumCoder);



    ResultT dispatchMap(Coder<?> keyCoder, Coder<?> valueCoder);



    ResultT dispatchSet(Coder<?> elementCoder);



    /** A base class for a visitor with a default method for cases it is not interested in. */

    abstract class WithDefault<ResultT> implements Cases<ResultT> {



      protected abstract ResultT dispatchDefault();



      @Override

      public ResultT dispatchValue(Coder<?> valueCoder) {

        return dispatchDefault();

      }



      @Override

      public ResultT dispatchBag(Coder<?> elementCoder) {

        return dispatchDefault();

      }



      @Override

      public ResultT dispatchCombining(Combine.CombineFn<?, ?, ?> combineFn, Coder<?> accumCoder) {

        return dispatchDefault();

      }



      @Override

      public ResultT dispatchMap(Coder<?> keyCoder, Coder<?> valueCoder) {

        return dispatchDefault();

      }



      @Override

      public ResultT dispatchSet(Coder<?> elementCoder) {

        return dispatchDefault();

      }

    }

  }

}